Type O blood protects against malaria

The most common blood type in the British population protects against the most deadly form of malaria, according to a study that heralds a new kind of treatment within a few years.

People with blood group O - around half of the UK population - are naturally protected from some of the most severe forms of the disease, which kill around two million people annually, according to a study at Edinburgh University.

The finding surprised the team, said Edinburgh's Dr Alex Rowe. "I found it amazing that malaria and blood groups have been studied for over 100 years but no one had looked in detail at the effects of blood group on life threatening malaria in Africa, where most malaria deaths occur."

The discovery points to new avenues of research for drugs or vaccines which recreate the protection offered by this blood type, she said, explaining that incidence of group O ranges from 40 per cent to 60 per cent, depending on the country.

Dr Rowe, with colleagues in the US, Mali and Kenya studied African children and found that those with blood type O were two-thirds less likely to experience unrousable coma or life-threatening anaemia.

Thus, if a drug could fully mimic this effect, it could cut the death toll "substantially - it's difficult to put a precise number on it because we didn't actually measure deaths, we measured life-threatening disease," she said.

The connection between blood type and death arises because red blood cells which are infected by malaria parasites block blood vessels which supply oxygen to the brain. Proteins from the parasite make the red blood cells sticky, forming "rosettes" that clog up microscopic blood vessels.

However, the team's findings published today in the Proceedings of the National Academy of Sciences suggest that group O red blood cells do not easily form the rosettes.

The scientists believe that creating drugs or vaccines which mimic the effect of having group O red blood cells by breaking up the rosette could dramatically reduce the severe and often fatal complications.

Dr Rowe said: "If we can develop a drug or a vaccine to reduce rosetting and mimic the effect of being blood group O, we may be able to reduce the number of children dying from severe malaria in sub-Saharan Africa."

The Edinburgh team has already developed a candidate drug to stop the rosetting, though it can cause bleeding. Dr Rowe said that she hoped a trial of this new approach to start within a few years, if funding can be found to back another generation of prototype drugs designed to overcome this side effect.

The research was funded by the Wellcome Trust and the US National Institutes of Health.